Pad selection in memory devices configured for stacked arrangements

ABSTRACT

Disclosed are various embodiments related to stacked memory devices, such as DRAMs, SRAMs, EEPROMs, and CAMs. For example, stack position identifiers (SPIDs) are assigned or otherwise determined, and are used by each memory device to make a number of adjustments. In one embodiment, a self-refresh rate of a DRAM is adjusted based on the SPID of that device. In another embodiment, a latency of a DRAM or SRAM is adjusted based on the SPID. In another embodiment, internal regulation signals are shared with other devices via TSVs. In another embodiment, adjustments to internally regulated signals are made based on the SPID of a particular device. In another embodiment, serially connected signals can be controlled based on a chip SPID (e.g., an even or odd stack position), and whether the signal is an upstream or a downstream type of signal.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of the following application, U.S.patent application Ser. No. 13/403,122, entitled “PAD SELECTION INMEMORY DEVICES CONFIGURED FOR STACKED ARRANGEMENTS,” filed on Feb. 23,2012, and which is hereby incorporated by reference as if it is setforth in full in this specification, and which also claims priority fromU.S. Provisional Patent Application Ser. No. 61/570,215, entitled“MEMORY DEVICES CONFIGURED FOR STACKED ARRANGEMENTS,” Attorney DocketNo, MCSJ-003P, filed on Dec. 13, 2011, which is hereby incorporated byreference as if set forth in full in this application fir gill purposes.

FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductormemory devices, and more particularly, to semiconductor memory devicesconfigured for stacked arrangements.

BACKGROUND

In many multichip arrangements, devices (e.g., integrated circuits,dice, or chips) may be placed in side to side configurations. Examplesof these types of arrangements include single in-line memory module(SIMM) and dual in-line memory module (DIMM) configurations. Othermultichip arrangements include multichip module (MCM) structures ofchips that may share a common package. However, such conventionalmultichip approaches may not be suitable for relatively large I/O anddensity structures. For these applications, vertical stacking usingthrough-silicon vias (TSVs) and die-to-die vias represents a morepromising technology. However, these technologies may be limited byvarious drawbacks and challenges related to on-chip circuitry for thestacked devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section diagram showing an example stacked memorydevice structure.

FIG. 2 is a cross-section diagram showing an example DRAM stackstructure with a memory controller.

FIG. 3 is a diagram showing an example DQ pad mapping for DRAMs in astacked arrangement.

FIG. 4 is a block schematic diagram showing an example pad selectorbased on a stack position identifier (SPID).

FIG. 5 is a cross-section diagram showing an example DRAM stack withtemperature and latency relationships.

FIG. 6 is a cross-section diagram showing an example pad,through-silicon via (TSV) and die-to-die via structure for multiplepads.

FIG. 7 is a block schematic diagram showing an example capacitancecomparator.

FIG. 8 is a timing diagram showing an example capacitance comparisonbetween adjacent pads.

FIG. 9 is a block schematic diagram showing an example automatic SPIDdeterminer using capacitance comparisons.

FIG. 10 is a cross-section diagram showing example internal supplyconnections across stacked DRAMs.

FIG. 11 is a block schematic diagram showing example selectors forconnecting internal supplies to inter-chip TSV connections during a testmode.

FIG. 12 is a block schematic diagram showing an example self-refreshcontroller based on SPID.

FIG. 13 is a block schematic diagram showing an example self-refreshoscillator adjustment based on SPID.

FIG. 14 is a block schematic diagram showing an example charge pump withVPP level adjustment based on SPID.

FIG. 15 is a block schematic diagram showing an example chip select andSPID matching circuit.

FIG. 16 is a diagram showing example latency variations for stackedmemory devices.

FIG. 17 is a block schematic diagram showing example latency adjustmentbased on SPID.

FIG. 18 is a cross-section diagram showing an example shared data strobesignal across stacked DRAMs.

FIG. 19 is a block schematic diagram showing an example data strobe paddriver based on a top of stack SPID.

FIG. 20 is a block schematic diagram showing an example data strobeadjustment based on a data strobe driven by the DRAM on the top of thestack of DRAMs.

FIG. 21 is a cross-section diagram showing an example serially connectedsignal through TSVs.

FIG. 22 is a schematic diagram showing example pad drivers for aserially connected signal through TSVs.

FIG. 23 is a schematic diagram showing example pad drivers for aserially connected signal through TSVs with on-chip signalmodifications.

FIG. 24 is a schematic diagram showing example bi-directional paddrivers based on upstream or downstream signaling for a seriallyconnected signal through TSVs.

FIG. 25 is a cross-section diagram showing example CAM devices withserially connected search key and search result signals.

FIG. 26 is a flow diagram showing an example method of performingsearches and providing results for stacked CAM devices.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction withparticular embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, etc. have not been described in detailso as not to unnecessarily obscure aspects of the present invention.

Some portions of the detailed descriptions which follow are presented interms of processes, procedures, block arrangements, logic blocks,functional blocks, processing, and/or other symbolic representations ofoperations or device arrangements. These descriptions andrepresentations are generally used by those skilled in the relevant artsto effectively convey the substance of their work to others skilled inthe art.

Particular embodiments can advantageously provide circuits, methods, andstructures, to facilitate circuit operation for stacked memory devices.For example, particular embodiments can advantageously provideapproaches that allow for devices to be manufactured using a same maskset and layout patterns regardless of a device's ultimate position in astack of memory devices.

Various embodiments relate to stacked memory devices, such as dynamicrandom access memories (DRAMs), static RAMs (SRAMs), electricallyerasable programmable read-only memories (EEPROMs), field-programmablegate arrays (FPGAs), and content addressable memories (CAMs). Forexample, identifiers that indicate a stack position of a device may beassigned or otherwise determined, and used by each memory device to makea number of adjustments on that device. In one embodiment, aself-refresh rate of a DRAM can be adjusted based on the SPID of thatdevice. In another embodiment, a latency of a memory device can beadjusted based on the SPID. In another embodiment, internal regulationsignals may be connected with other devices by way of through-siliconvias (TSVs) and control circuitry, such as when operating in a testmode. In another embodiment, adjustments to internally regulated signalscan be made based on the SPID of a particular device. In anotherembodiment, serially connected signals can be controlled based on a chipSPID (e.g., an even or odd stack position), and whether the signal is anupstream or a downstream type of signal. These and various otherembodiments will be discussed in more detail below.

Referring now to FIG. 1, shown is a cross-section diagram 100 of anexample stacked memory device or “3-D” structure. In this example,memory controller 102 can support a number of DRAM devices (e.g.,DRAM-0, DRAM-1, DRAM-2, . . . DRAM-N) arranged in a stackedconfiguration. Memory controller 102 may represent any processing orlogical computing device, as well as any common interface for the memorydevices stacked thereon. Underfill/bumps 104 can include C4 bumps andunderfill for connection to the DRAMs. Encapsulation 106 may encapsulatethe stacked DRAMs, and the structure may be capped by heat spreader 108.For example, heat spreader 108 can be an integrated heat spreader (IHS).

Interconnections between one or more of the DRAMs and memory controller102 can be accommodated by use of through-silicon vias (TSVs) 110 and/ordie-to-die vias 112. TSVs 110 may also include thermal TSVs (TTSVs) foruse in managing heat dissipation, and reducing temperature differences,within structure 100. In addition, interlayer dielectric (ILD) andsignal layers may also be included in the regions between the DRAMs.However, pad arrangements and associated control circuitry on each chipin particular embodiments can allow for simplified signal layer routing,or in some cases the complete removal of such a signal layer.

While memory controller 102 is shown, any suitable interface chip ordevice is contemplated in certain embodiments. Any type of memoryinterface chip, processor, type of controller, switch fabric, othermemory chip, optical processing layer, or package substrate, can beutilized in place of memory controller 102 in some applications.Further, while pads described herein may include metal pads or otherconnections to TSVs, particular embodiments may also not include actualmetal pads, but rather other types of connections to TSVs. For example,pads can include connections below a surface of a semiconductor device,such as when a connection layer (e.g., layers of metallization forsignal connections) is used between a TSV and the semiconductor devicesurface. However, metal pads on a semiconductor surface may be desirableso that the probe testing as part of a test flow (e.g., including finaltest, etc.) can be performed to determine known good die (KGD) prior toplacing the die in a stack to form a stack the memory devices. In anyevent, “pads” as described herein can represent any interconnectposition on a semiconductor device. As will be discussed in more detailbelow, testing may also be performed once the memory devices are securedin a stack.

TSVs can be formed using any suitable fabrication process. For example,a front-end-of-line (FEOL) process that creates active devices canproceed or follow TSV formation. In this case, wafer thinning to exposethe TSVs on a wafer backside can occur with a back-end-of-line (BEOL)process that creates conductive lines for power and signals betweendevices and off-chip connections. In another example, TSV formation canoccur from the wafer backside after device wafer fabrication andthinning. TSVs and/or die-to-die vias can be filled with any suitableconductive material (e.g., doped polysilicon, tungsten, copper, etc.).In any event, particular embodiments are suitable for stacked memorydevices utilizing TSV, die-to-die via, as well as other chipinterconnections.

TSV processing steps can include via etch or drill, an insulator andseed layer deposition, and via fill. The via etch step can include adeep reactive ion etching (DRIE) process, or a laser etching processusing ultraviolet lasers. The insulating layer may include SiO₂, and maybe deposited using chemical vapor deposition (CVD) techniques. Organiclayers (e.g., parylene) may also be utilized as an insulating layer insome embodiments. Also, a diffusion barrier layer (e.g., TiN) may followdeposition of the insulating layer. A seed layer (e.g., TiN and Cu) maythen be deposited (e.g., via CVD techniques) to facilitate metallizationin the TSV. The TSV may then be filled, such as by depositing tungstenusing a CVD process, or electrochemical plating for coppermetallization. Of course, other methods and materials as to TSV,die-to-die via, and/or other chip interconnections can also be employedin particular embodiments.

In addition, while TSVs and die-to-die vias are discussed in variousexamples herein, other types of connections suitable forinterconnections among stacked devices can also be employed inparticular embodiments. For example, one or more signal layers,interposers, or other substrates can be utilized between memory devicesin the stack. Also, TSVs may be mated to microbumps that may then beconnected to other TSVs and/or a signal layer or substrate. Thus,particular embodiments are suitable to a variety of types ofinterconnections between chips that are stacked on top of one another.

Particular embodiments are suited to chips or devices that may notutilize different mask patterns based on an ultimate position in a stackof memory devices. In this way, high-volume manufacturing of individualmemory devices can occur without regard to possible applications for thememory devices that might include stacked arrangements. This isaccomplished by design techniques that allow each memory device to adaptdynamically to any position in the stack of memory devices.

Referring now to FIG. 2, shown is a cross-section diagram 200 of anexample DRAM stack structure with a memory controller. In this example,eight DRAM memory devices (e.g., DRAM-0, DRAM-1, . . . DRAM-7) arestacked on top of underfill/bumps 104 and memory controller 102. Addressand control signal TSVs 202, which may also include die-to-die vias 206,may be used for signals carried from memory controller 102 to each DRAM.DQ signal TSVs 204, which may also include die-to-die vias 206, can beused to form a given connection to a corresponding DRAM device. Thisparticular structure can be used in a wide I/O applications whereby theI/Os supplied by each individual DRAM are connected in parallel fashion.For example, if each DRAM is configured in a 16-bit I/O configuration,parallelizing these I/Os across eight chips may provide a module with a128-bit I/O configuration. Similarly, if each DRAM is configured in a64-bit configuration, the module can be configured as a 512-bitconfiguration. Of course, any number of memory devices (e.g., 2, 4, 8,16, etc.) in the stack, and any DQ configurations (e.g., 4, 8, 16, 32,64, 128, 256, -bits, etc.), can be accommodated in particularembodiments.

The particular example of FIG. 2 actually shows a corresponding DQsignal for each memory device. Also, each memory device may bemanufactured with the same mask set or set of layout patterns. Thus inthis example, a single on-chip DQ or data path may be mapped to eightdifferent positions (e.g., possible pad connections) on that chip inorder to accommodate any positioning within the memory device stack. Onealternative way to accomplish this is to design a separate BEOL or metallayer/pad structure for each memory device based on its ultimateposition in the memory stack. However, it may not be desirable tomaintain eight separate memory device manufacturing and/or test lines.This problem only gets worse as chip stacking and interconnecttechnology improves to allow a higher number of devices to be stacked.As such, a single device manufacturing/test flow whereby each memorydevice is adaptable to any position in the DRAM stack is desirable.Particular embodiments provide on-chip controls in order to drivedifferent DQ pad positions without necessarily having to distinguish thedevices during semiconductor processing, sort, or test based on a stackposition. In this way, the manufacture of each DRAM device can beperformed by using a same mask set and layout patterns, and traditionalper-single-chip test methodologies.

In particular embodiments, multiple pads (e.g., different pads orexternal interconnect positions) that are allocated to a same signal canbe configured on a memory device based on a stack position. In oneembodiment, a semiconductor memory device can include: (i) a pluralityof pads allocated to a signal on the semiconductor memory device; (ii) astack position identifier for identifying a position of thesemiconductor memory device in an aligned vertical stack of a pluralityof semiconductor memory devices; and (iii) a pad selector configured toselect one of the plurality of pads to be connected to the signal on thesemiconductor memory device in response to the stack positionidentifier, where the pad selector is configured to disconnect each of aremaining of the plurality of pads from the signal based on the stackposition identifier.

Referring now to FIG. 3, shown is a diagram of an example DQ pad mappingfor DRAMs in a stacked arrangement. Each mapping 300 shows an examplepad (e.g., a metal pad) or connection position mapping for a given DRAMin the stack. These mappings represent examples of mappings for a givenpad or other type of connection interface suitable for connecting withother devices. For example, each of pads 302 can be configured toconnect to another device by way of one or more die-to-die vias and/orone or more TSVs, and the connections may be direct or through othercircuitry. In particular embodiments, such a mapping of different padsor interconnection positions on a memory device can be controlledon-chip based on a stack position of that chip. This may be in additionto external connectivity based on die-to-die vias, signal layers, and/orTSVs.

When viewed in conjunction with FIG. 2, FIG. 3 shows one example mappingfor a DQ signal, whereby an enabled pad or interconnect position iscontrolled based on a position of the DRAM in the stack. For example, asshown in 300-0, DRAM-0 has only a leftmost pad enabled for the DQ signal(indicated by a shaded circle on the leftmost pad [see also, e.g.,304]), while each of the remaining seven pads in the mapping areisolated from the DQ signal (isolations are indicated by “X” on thesignal lines). A circle in the square pad (see, e.g., 306) can indicatea die-to-die via and/or TSV connection thereto. Thus, because DRAM-0 isat the bottom of the stack of eight DRAMs, each pad or interconnectionposition map to the DQ signal may be connected to a die-to-die viaand/or a TSV. However, particular embodiments allow for control suchthat only one of the eight pads (e.g., a leftmost or first pad for theDRAM-0 in the mapping are enabled for that DRAM. As a result, excesscapacitance due to the inter-chip connections on alternative padpositions can be substantially cut-off.

Similarly, as shown in 300-1, a next in stack DRAM-1 can have a next inline pad (e.g., second pad from the left) enabled, while others in themapping are disabled. Note also that the leftmost pad in DRAM-1 may nothave a die-to-die via or connection to the TSV, while other pads in themapping do. Note also that the DQ signal described here may represent aninternal data input and/or output signal, and may be a signal that wouldotherwise connect to the pad absent electrostatic discharge (ESD) and/ordriver or other input path and/or output path control circuitry. Assuch, the DQ signal may represent any signal internal to the chip thatmay be mapped to one of eight (or any number of) pads or interconnectpositions on a given memory device. As described herein, thisarrangement represents one example of mapping an internal signal forconnection on different external paths as a result of a stack positionof the device.

As shown in 300-2, DRAM-2 may have a next in line pad enabledconnection, and so on up the stack for DRAM-3 as shown in 300-3, DRAM-4as shown in 300-4, DRAM-5 as shown in 300-5, DRAM-6 as shown in 300-6,and DRAM-7 as shown in 300-7. As shown in 300-7, each of eight pads orexternal connection positions 302-0, 302-1, . . . 302-7 can be mapped toa single DQ signal. In the case of DRAM-7, a rightmost pad connectionmay be enabled for a path between DRAM-7 and memory controller 102. Asshown in 300-7, each of the remaining possible pad connections in theleftmost seven positions can be disabled as a result of control based onthe stack position. In this way, each DRAM or other memory device in thestack of devices can be customized to external (i.e., inter-chip)connections by enabling different possible interconnect positions in amapping to a common signal (e.g., a DQ signal) based on stack position.

Of course, while eight DRAMs and eight DQ pad mappings are shown in thisparticular example, any number of memory devices and mappings to acommon on-chip signal can be accommodated in particular embodiments. Inaddition, the memory devices in the stack of memory devices can beoriented either right side up or upside down. Further, references to“top,” “bottom,” “up,” “down,” “upstream,” “downstream,” “on top of,”“above,” “below,” “vertical,” “adjacent,” etc., are made with referenceto other devices in a stack of devices, and do not limit the inventionto a particular orientation of the entire stack of devices, but arerather directed to relative positioning of the devices in a stack ofmemory devices, as well as any associated substrates, controllers, andthe like.

Referring now to FIG. 4, shown is a block schematic diagram 400 of anexample pad selector based on a stack position identifier (SPID). Aswill be discussed in more detail below, SPIDs can be programmed,assigned, or otherwise determined (e.g., automatically) for each memorydevice in a stack of such devices. In the example followed herein foreight DRAM devices, three SPID bits can be used to uniquely identifyeach DRAM in the stack based on its position in the stack. A widevariety of storage options can be used for storing the SPID values. Forexample, nonvolatile memory can be used, SRAM bits, or other latches,etc., can be used in certain embodiments. In one example, the SPID bitscan be fuse-programmable, such as prior to or around the time of astacking of such devices. In another example, the SPID bits can be metalprogrammable, but this would require different metal layout patterns foreach stack position. As will be discussed in more detail below, certainembodiments also contemplate an automatic SPID detection or assignmentafter the memory devices are placed in a stack. In any event, an examplecorrelation of SPID bits per memory device stack position is shown belowin Table 1.

TABLE 1 Memory Device Position SPID[2] SPID[1] SPID[0] DRAM-0 0 0 0DRAM-1 0 0 1 DRAM-2 0 1 0 DRAM-3 0 1 1 DRAM-4 1 0 0 DRAM-5 1 0 1 DRAM-61 1 0 DRAM-7 1 1 1

Based on the SPID (e.g., bit values as shown in Table 1), pad selectorscan be used to isolate various pads or interconnect positions from theDQ signal. This selection may effectively remove excess capacitance dueto the inter-chip connections on alternative pad positions (e.g., padpositions 302-0, 302-1, . . . 302-6 in 300-7 of FIG. 3). A “pad” asdescribed herein may represent an actual metal pad (e.g., a pad that canbe probed), or any position configured for an interconnect to anotherchip. As discussed above, any signal mapping to a plurality of pads, orto different interconnect positions, based on a stack position, and inparticular a stack position identifier, can be accommodated inparticular embodiments. In the particular example of FIG. 4, padselector 402 can be coupled to each pad or interconnect position 302. Asshown for pad 302-0, associated pad selector 402 can include a pass gateformed by PMOS transistor 414 and NMOS transistor 416. NAND gate 410 canreceive inverted SPID bit signals by way of inverter 404 for SPID[2],inverter 406 for SPID[1], and inverter 408 for SPID[0]. An output fromNAND gate 410 can control transistor 414, while an inverted output viainverter 412 can control transistor 416.

In this example, pad position 302-0 may be disabled for this DQ signalunless SPID=000, representing the lowest memory device in the stack(see, e.g., 300-0 in FIG. 3). The pad selectors 402 can thus beprogrammed for each pad position 302 in order to control enabling anddisabling of each such pad position 302 that is mapped to acorresponding DQ signal. For example, this DQ signal pad arrangement maybe replicated for each data I/O for a particular memory device (e.g., 16times for a 16-bit I/O DRAM). Depending on the stack position (e.g., viaSPID) of a given DRAM in a stack of memory devices, only one of such padpositions 302 may be selected by pad selector 302 for each such DQsignal on a memory device.

In addition, pad selection circuitry may be replicated for differentsignals. For example, such pad selection circuitry may be shared amongdifferent DQ signals on a same memory device. This is because a givenselection (e.g., 1 of 8) of pad positions may be the same for each suchsignal (e.g., DQ0, DQ1, DQ2, . . . DQ15). Alternatively, pad selectioncircuitry 400 may be replicated for each mapping of common signals andpads. Further, pad selection circuitry 400 may also be used to steer aredundant pad path to replace that of a de-allocated memory device, suchas where a top memory device in the stack may replace a de-allocatedmemory device in the stack. Also, as one skilled in the art willrecognize, other digital logic or circuitry can be employed in order toachieve a similar type of decoding. In addition, various ESDconsiderations may also be accounted for in the design of pad selectioncircuitry in particular embodiments.

Referring now to FIG. 5, shown is a cross-section diagram 500 of anexample DRAM stack with temperature and latency relationships. Asindicated in this example stack of DRAM devices, as one goes up thestack, generally an increase in temperature may occur. As discussedabove with respect to FIG. 1, temperature may be managed by use of aheat spreader 108, as well as by use of various thermal TSVs (TTSVs).These may help in equalizing temperature differences across memorydevices in the stack, but may also result in increased die sizes and/orincreased temperature differences across a same chip. In addition,various adjustments to internal circuitry based on SPID can be made incertain embodiments in order to accommodate such an anticipatedtemperature increase. Other effects associated with stacked memorydevices include increased latency as one goes up the stack. This latencycan be seen on various control and/or data signals. As will be discussedin more detail below, various latency adjustments can be made based onSPID in certain embodiments in order to effectively even out latencydifferences as seen at a memory interface chip (e.g., controller 102) orsubstrate.

Referring now to FIG. 6, shown is a cross-section diagram 600 of anexample pad, TSV, and die-to-die via structure for multiple pads. Thisshows one example of possible connections between pads 302 at differentpositions on each device, with connections through other devices tomemory controller 102. Of course, other circuitry or other connectionsor paths/arrangements may be included relative to TSVs 204, die-to-dievias 206, and underfill/bumps 104 (e.g., including balls or C4 bumps602). Also, different relative dimensions, number of devices, orderingof pads, and common signals that map to a plurality of pads, arecontemplated in particular embodiments. In any event, the example ofFIG. 6 shows that a DRAM at a higher position (e.g., DRAM-7) in thestack may have a longer path to memory controller 102 as compared to aDRAM at a lower position (e.g., DRAM-1) in the stack.

In particular embodiments, stack position identifiers can beautomatically determined based on a sensing of the connections on padsthat are mapped to a common signal. In one embodiment, a method ofdetermining a stack position of a semiconductor memory device, caninclude: (i) comparing, for each of a plurality of pads allocated to asame signal on the semiconductor memory device, a first capacitance on afirst pad against a second capacitance on a second pad; (ii) setting alatch if the second capacitance is greater than the first capacitance byat least a predetermined amount; (iii) counting a number of the latchesthat remain reset to determine a stack position identifier for thesemiconductor memory device; and (iv) storing the stack positionidentifier in a register on the semiconductor memory device.

In this way, stack position identifiers can automatically be determinedby each memory device in the stack of memory devices based on comparingcapacitances between associated pads. This allows for determination ofstack positions by using circuitry found on each memory device, withouthaving to program any stack position identification in advance. Certainembodiments provide for determination of a device's position in a stackof devices after the devices have been placed in the stack. Thus, stackpositions can be determined based on connections made external to thememory device, where those connections may be in furtherance of amultiple pad to same signal mapping as part of a stack memory devicestructure.

Referring now to FIG. 7, shown is a block schematic diagram 700 of anexample capacitance comparator. This particular circuit represents oneexample of a circuit for comparing capacitance in order to determine astack position. When viewed in conjunction with FIG. 6, it can beappreciated that different pads (e.g., adjacent pads) may have differentcapacitances by virtue of the connections (e.g., TSVs 204, die-to-dievias 206, etc.). As such, pad 302-A and 302-B may represent adjacentpads, as will also be discussed below with reference to FIG. 9.

In the example circuit of FIG. 7, a data value (e.g., high, low, apredetermined voltage, etc.) for application to pad 302-A can beprovided by a capacitance test data signal (e.g., CTDA) when enabled bytest mode enable signal CTEN. For example, CTEN can be triggered off apower-up detect signal so that each device in the stack can determineits SPID upon power up. As another example, CTEN can be generatedglobally (e.g., from memory controller 102) for each chip to perform thecapacitance comparison for automatic SPID determination. In some cases,CTDA may be a substantially static data value, while CTEN is a pulsedsignal.

An example circuit to drive a high or low value (from CTDA) onto pad302-A while CTEN is high, and to tri-state when CTEN is low, may includeNAND gate 702-A, PMOS transistor 708-A, NOR gate 704-A, inverter 706-A,and NMOS transistor 710-A. A similar circuit that may be used to drive ahigh or low value (from CTDB) onto pad 302-B while CTEN is high, and totri-state when CTEN is low, may include NAND gate 702-B, PMOS transistor708-B, NOR gate 704-B, inverter 706-B, and NMOS transistor 710-B. Duringoperation, CTDA and CTDB may be set to opposite values such thatsubstantially equally differing levels are applied to pads 302-A and302-B during the CTEN pulse.

Referring also to FIG. 8, shown is a timing diagram 800 of an examplecapacitance comparison between adjacent pads, such as using the circuitof FIG. 7. In FIG. 8, an example operation of pulsed signal CTEN isshown in waveform 802, while an example operation of CTDA is shown inwaveform 804 as being set low prior to the CTEN pulse, and an exampleoperation of CTDB is shown in waveform 806 is being set high prior tothe CTEN pulse.

At the falling edge of CTEN, an edge-triggered pulse CSEN indicatingthat capacitance sensing is enabled may be generated as shown in examplewaveform 808. For example, CSEN may be generated using delay circuit712, inverter 714, and NOR gate 716 to generate a positive goingedge-triggered pulse having a width of about that of delay circuit 712.For example, the delay of delay circuit 712 may be long enough to ensureadequate time to complete the charge sharing process between pads 302-Aand 302-B. When CSEN is high (e.g., during the pulse) and its complimentis low via inverter 722, the pass gate formed by NMOS transistor 718 andPMOS transistor 720 can be enabled to allow charge sharing to occurbetween pads 302-A and 302-B. Because CSEN may not be triggered until afalling edge of CTEN, pass gate 718/720 may only be enabled when CTEN islow. Thus, pads 302-A and 302-B may be coupled together for chargesharing purposes only when the circuits that drive data onto the padsare tri-stated. For example, when CTEN is low, transistors 708-A and710-A for pad 302-A, and transistors 708-B and 710-B for pad 302-B areoff to place each path in tri-state.

An example of this charge sharing mechanism on pads 302-A and 302-B isshown respectively as waveforms 810-A and 810-B. In this particularexample, both of pads 302-A and 302-B start out low, but pad 302-B maybe charged high via transistor 708-B when CTEN is high. Thus in thisexample, CTDA may be low and CTDB may be high, as shown in respectivewaveforms 804 and 806. Once CTEN goes low and CSEN goes high to enablecharge sharing between pads 302-A and 302-B, some intermediate voltagelevel can be established at the positive input of differential amplifier724. As shown in example waveform 810, this intermediate voltage levelafter charge sharing may be higher than a middle value between the highand low levels applied, thus indicating that pad 302-B has a highercapacitance than pad 302-A.

Differential amplifier 724 may be used to compare the charge sharedvalue input to a positive terminal against a predetermined referencelevel, V_(REF). For example, if the charge shared value is greater thanV_(REF), then the differential amplifier output (DAOUT) may be high, butif the charge shared value is less than V_(REF), then DAOUT may be low.In order to ensure that differential amplifier 724 performs thiscomparison after the charge sharing is complete, a differentialamplifier enable signal (DAEN) can be generated after a falling edge ofCSEN. Thus, the falling edge of CSEN may trigger a high going pulse onDAEN by, for example, using the edge triggered pulse generation circuitthat includes delay circuit 728, inverter 730, and NOR gate 732.Waveform 812 shows an example operation of DAEN, which can pulse highupon a falling edge of CSEN.

Once DAEN is high, NMOS transistor 726 may allow current to flow throughand/or otherwise enable differential amplifier 724 such that DAOUT mayprovide an accurate output. DAEN may also be used with inverter 738 toopen a pass gate formed by NMOS transistor 740 and PMOS transistor 742to capture the value of DAOUT. When pass gate 740/742 is open by DAENbeing high, which also enables differential amplifier 724, a value ofDAOUT (see, e.g., waveform 814) can override the value stored in thelatch formed by inverters 734 and 736. The output of latch 734/736 canbe buffered by inverters 744 and 746 to provide output signal DBCH (see,e.g., waveform 816). For example, DBCH may go high to indicate that thecapacitance at pad 302-B is greater than the capacitance at pad 302-A.Conversely, DBCH may be low the capacitance at pad 302-A were detectedas greater than the capacitance at pad 302-B.

In this way, a capacitance comparison between two pads, or otherexternal connection interfaces, can be performed in particularembodiments. Further, such capacitance comparison circuits may beemployed as part of a test mode and/or as part of a standard power-upsequence. In certain embodiments, test modes and/or power-up sequencescan include a sequenced activation for each memory device in the stackso that capacitance comparisons on a given chip are not interfered withby capacitance comparisons ongoing on a different chip. Further, suchcapacitance comparisons may be employed for other pad pairs, such asthose that may not be mapped to a same signal. This may be useful aspart of a test mode to detect external (e.g., TSV connections, etc.) ondifferent pad or external connection pairs.

A test mode for capacitance comparisons may also be performed todetermine whether a given pair of pads (e.g., pads 302-A and 302-B) havea same or matching capacitance. For example, matching capacitances canbe determined by adjusting the level of V_(REF) and/or by performingmultiple tests with different values on CTDA and CTDB (e.g., first ‘1’and ‘0’, then ‘0’ and ‘1’). In this way, external connections to TSVs ona given device can be tested by using a test mode on that memory device.Further, other types of comparisons, such as resistance orcurrent-based, as opposed to capacitance-based, may also be employed inparticular embodiments.

Referring now to FIG. 9, shown is a block schematic diagram 900 of anexample automatic SPID determiner using capacitance comparisons. Inorder to determine SPID values for a given memory device, capacitancecomparisons may be made for adjacent pads. For example, a given set ofpads (or any external connection interface) that may be mapped to a samesignal are shown as pad 302-A, pad 302-B, . . . pad 302-H. For example,pads 302-A, 302-B, . . . 302-H, may correspond to pads 302-0, 302-1, . .. 302-7 (see, e.g., 300-7 in FIG. 3). Also, a pad 302-X can be includedfor comparison with a first or end pad 302-A. For example, 302-X may bea test pad with or without extra external connections.

Example capacitance comparison circuits 700, as discussed with referenceto FIGS. 7 and 8, may be used to compare each pair (e.g., an adjacentpair) of pads. For example, capacitance comparator 700-AB may be used toperform a capacitance comparison between pads 302-A and 302-B.Similarly, capacitance comparator 700-DE may be used to perform acapacitance comparison between pads 302-D and 302-E. Counter 902 mayreceive outputs from each of capacitance comparators 700, and may counta number of zeros to produce a 3-bit output based on the supplied clock,CLK. For example, CLK may be supplied in response to the test mode(e.g., that activates CTEN) and/or as part of power up sequencing. CLKactivation may also be controlled to ensure that capacitance comparatoroutputs (e.g., DBCH of FIGS. 7 and 8) are settled prior to enabling thecounting.

Once the count of zeros is completed, these values may be stored in SPIDregisters 904 to supply identifier bits SPID[2], SPID[1], and SPID[0].Once the SPID register values are updated, SPID_Ready may be activatedto indicate that the values stored in SPID registers 904 are ready foruse. For example, SPID_Ready may be low to disable various circuits fromusing SPID values, and then may be brought high to indicate that SPIDvalues are ready for use. An example of such zero value countingcorresponding to SPID values is shown below in Table 2. Alternatively,“1” values may also be counted, or other correlations between adjacentpad capacitance determinations and ultimate SPID values can beperformed. This particular example applies to the example externalconnection arrangement as shown in FIG. 6, but other types of externalaction arrangements, such as any other pattern for connecting a set ofpads or as external connection interfaces that are mapped to a samesignal, may also be accommodated.

TABLE 2 Device Comp XA, AB, BC, CD, DE, EF, FG, GH SPID[2:0] DRAM-011111111 000 DRAM-1 01111111 001 DRAM-2 00111111 010 DRAM-3 00011111 011DRAM-4 00001111 100 DRAM-5 00000111 101 DRAM-6 00000011 110 DRAM-700000001 111

SPID registers 904 may also be part of, or otherwise associated with, amode register, such as a mode register on a double data rate (DDR) DRAM.In one embodiment, default values may be stored in SPID registers 904and/or the associated mode register positions for SPID. For example, amode register may contain designated bits for SPID, or any other uniqueID for each of a group of memory devices in a stack. The mode/SPIDregister may have a default setting upon power-up whereby each memorydevice in the stack has a same initial SPID value (e.g., SPID=000).Then, each command may be applied and recognized by each memory deviceof the stack. SPIDs for each memory device can subsequently be assignedor determined, such as by using the approach described above.

In one example, SPID registers 904 may contain resettable values toallow for commands to be accepted by each device in the stack ofdevices. For example, a mode register may be programmed to indicate atest mode or global command configuration, whereby SPID registers 904are subsequently reset to a given value in response thereto. Thisapproach provides an override mechanism for SPID registers 904 that canthen be undone upon completion of the particular test mode or globalcommand operation. For example, the determined SPID values could bestored in one latch and preserved throughout the test mode or globalcommand configuration that overrides the SPID values, such that thedetermined SPID values could be restored thereafter. A control signalcan be used to control a multiplexer to select either a stored SPIDvalue from SPID registers 904, or an override value supplied via a moderegister. As another example, a separate control signal (e.g., a globalchip select signal) can be used when asserted to override SPID values toallow a same command to be accepted by each memory device in the stack.

Other example approaches for automatically determining SPID values canalso be employed in certain embodiments. For example, a sequential SPIDassignment approach may include use of a serially connected signal, aswill be discussed below. In such connections, each memory device canreceive a signal from an adjacent memory device, and perform operations(e.g., data modification, combinatorial logic, clocking adjustments,etc.) thereon. For example, given default SPID values of zero, an SPIDvalue may be sent from one memory device to a next memory device locatedabove in the stack of memory devices, and the receiving device mayeffectively add one to the received value, and then store that value asits SPID. Thus, each device can sequentially assign itself an SPIDvalue. Certain embodiments may also support such a serially assignedSPID comparison mode against an SPID determined through another approach(e.g., capacitance comparison), as a way to double check SPIDdetermination. For example, an error indication may be generated if suchvalues do not match.

Also in particular embodiments, a test mode can connect one or more ofvarious internal supplies together for one or more devices in a stack ofdevices. In one embodiment, a semiconductor memory device can include:(i) a stack position identifier for identifying a position of thesemiconductor memory device in an aligned vertical stack of a pluralityof semiconductor memory devices, where the plurality of semiconductordevices are coupled together via a common vertical connection; (ii) atest mode detector configured to determine a test mode in response to areceived command and a match of the stack position identifier againstthe received command; (iii) a supply generator configured to generate aninternal supply for the semiconductor memory device; and (iv) a supplycoupler configured to couple the internal supply to the common verticalconnection in response to the determined test mode.

Referring now to FIG. 10, shown is a cross-section diagram 1000 ofexample internal supply connections across stacked DRAMs. Exampleinternal supplies for DRAMs include negative bulk supply VBB, word linehigh level VPP, and other internal regulated levels, such as for thememory array, any of which may be represented here as VREG. In certainembodiments, one or more of pads 302, TSVs 204, and die-to-die vias 206can be used to implement or allow common vertical connections to eachDRAM and memory controller 102. Metal pads may be optional, butdesirable due to accommodating probe level testing. Of course, othersuitable patterns, internal supplies, etc., can have connections (e.g.,common vertical connections) provided for as well.

One or more of the memory devices, such as DRAM-5 (see, e.g., 1002) andDRAM-3 (see, e.g., 1004) may have their internal supplies connected toan appropriate common vertical connection to allow for testing and/ormonitoring via memory controller 102. In this way, internal supplygeneration circuits may be tested once the memory devices are placed ina stacked configuration. In addition, this configuration may also allowfor an override of the internal supply of one or more memory devices inorder to test the effects of different supply values. In this case, theinternal supply circuitry may be disabled by this test mode for a givenchip in order to allow for the override. Furthermore, if it isdetermined that a particular internal supply regulator has failed afterthe devices have been secured in the stacked configuration, this failedregulator may be supplemented or effectively replaced by anotherfunctioning regulator in a different device in the stack. For example,if the VPP charge pump is determined to have failed on DRAM-3, the VPPcharge pump for DRAM-5 or an adjacent DRAM, may be connected to the VPPsupply for DRAM-3 via the appropriate common vertical connection.Further, control for regulators of different chips in the stack mayutilise SPIDs. In this way, a level of redundancy may be provided forinternal supplies across memory devices.

In certain embodiments, test modes can allow for one, two, or any numberof memory devices in a stack to connect internal supplies to a commonvertical connection. For example, one test mode may provide for asequential connection of a designated internal supply to a commonvertical connection such that memory controller 102 or a test system maytest a regulated supply from each memory device in the stack. Thesequencing, which may be in any order of memory devices, such as apre-programmed or random ordering of memory devices, can be controlledby use of SPIDs. For example, the test mode can be generated by a testdevice or memory controller 102, and associated test commands may beissued with an SPID designating that an internal supply be connected toa common vertical connection. In this way, internal supplies from eachmemory device in a stack of memory devices can be measured via a testmode after the memory devices are placed into the stack.

Referring now to FIG. 11, shown is a block schematic diagram of exampleselectors for connecting internal supplies to inter-chip TSV connectionsduring a test mode. As shown here in 1102, VPP test pad 1110 mayrepresent the common vertical connection mapped to the VPP supply inFIG. 10. Similarly, VREG test pad 1120 shown in 1104 may represent thecommon vertical connection mapped to the VREG supply in FIG. 10, and VBBtest pad 1130 shown in 1106 may represent the common vertical connectionmapped to the VBB supply in FIG. 10. As noted above, other supplies orinternal signals can also be mapped or allocated for possible connectionto common vertical connections across stacked memory devices.

In 1102, VPP generator 1108 may normally be used to generate word linehigh supply VPP. In this example, test mode signal TMVPEXT may be usedto indicate connection of VPP test pad 1110 to internal supply VPP byPMOS transistor 1112. Level shifter 1116 may be used to shift from aVDD-based signal (e.g., TMVPEXT) to a VPP or VPP+ (e.g., a level atleast as high as VPP or the level of VPP test pad 1110, so as not toforward bias a P-N junction of transistor 1112), and inverter 1114 mayalso be supplied at this VPP+ level. In a mode whereby the signal at VPPtest pad 1110 is to override the internally generated VPP supply,TMVPEXT may be used to disable VPP generator 1108. However, TMVPEXT orother suitable test mode and/or control signals may also be used toindicate to VPP generator 1108 that it needs to enable additional orredundant charge pump capabilities therein, such as when VPP generator1108 is to act in a redundant capacity for a different DRAM device, asdiscussed above.

In 1104, internal voltage regulator 1118 may normally be used togenerate regulated supply VREG. In this example, test mode signalTMVREXT may be used to indicate connection of VREG test pad 1120 tointernal supply VREG by the pass gate formed by NMOS transistor 1122 andPMOS transistor 1124. Inverter 1126 may be used to control PMOStransistor 1124 and in complementary fashion to control NMOS transistor1122. In a mode whereby the signal at VREG test pad 1120 is to overridethe internally generated VREG supply, TMVREXT may be used to disableinternal voltage regulator 1118. However, TMVREXT or other suitable testmode and/or control signals may also be used to indicate to internalvoltage regulator 1118 that it needs to enable additional or redundantsupply capabilities therein, such as when internal voltage regulator1118 is to act in a redundant capacity for a different DRAM device, asdiscussed above.

In 1106, VBB generator 1126 may normally be used to generate bulk lowsupply level VBB, to reverse bias P-WELLS under the memory cells forcell leakage reduction. In this example, test mode signal TMVBEXT may beused to indicate connection of VBB test pad 1130 to internal supply VBBby NMOS transistor 1132. Negative level shifter 1134 may be used toshift from a VDD-based signal (e.g., TMVBEXT) to a VBB or VBB− (e.g., alevel at least as low or negative as VBB or the level of VBB test pad1130. In a mode whereby the signal at VBB test pad 1130 is to overridethe internally generated VBB supply, TMVBEXT may be used to disable VBBgenerator 1126. However, TMVBEXT or other suitable test mode and/orcontrol signals may also be used to indicate to VBB generator 1126 thatit needs to enable additional or redundant negative charge pumpcapabilities therein, such as when VBB generator 1126 is to act in aredundant capacity for a different DRAM device, as discussed above.

Thus, each of VPP generator 1108, internal voltage regulator 1118, andVBB generator 1126 may be designed such that additional regulation orpumping capabilities may be enabled to support other memory devices inthe stack via an appropriate common vertical connection. Further, eachof VPP generator 1108, internal voltage regulator 1118, and VBBgenerator 1126 may be designed to be disabled under certain situations,such as when it is to be replaced by a corresponding regulator/generator(e.g., one with enhanced regulating or pumping capabilities enabled)from another memory device and the stack.

In particular embodiments, SPID bits may be used in order to isolatewhich memory devices are to be configured in a test mode, such as in asupply override test mode, or a redundant supply test mode, etc., asdiscussed above. For example, circuitry to generate various test modesignals (e.g., TMVPEXT, TMVREXT, TMVBEXT, etc.) may be generated by useof chip select signals sent with the test mode command (e.g., frommemory controller 102) matching with the SPID of a particular device. Asanother example, bit settings to provide a mapping as to the types ofsupply accesses via a common vertical connection may also be utilized.For example, a table that includes SPIDs and corresponding settings,such as VPP override, VBB override, providing redundancy for a deviceidentified by different SPID, etc., may be utilized in order to managevarious supply related test modes. In some applications, such a tablemay be stored on memory controller 102 such that test mode or other suchregulator setting commands as discussed herein may be sent to the propermemory devices for configuration of the supplies by use of and SPIDscorresponding common vertical connections.

In various embodiments, a self-refresh timing adjustment can be madebased on a position of a device in a stack of such devices. In oneembodiment, a semiconductor memory device can include: (i) a stackposition identifier for identifying a position of the semiconductormemory device in an aligned vertical stack of a plurality ofsemiconductor memory devices; (ii) a self-refresh oscillator configuredto generate an oscillating signal to control a rate of self-refreshoperations for the semiconductor memory device; and (iii) an oscillatoradjustor configured to increase the self-refresh oscillator from a firstfrequency to a second frequency in response to the stack positionidentifier when the stack position identifier indicates that thesemiconductor memory device is higher in the aligned vertical stack thanat least one of the plurality of semiconductor memory devices.

Referring now to FIG. 12, shown is a block schematic diagram 1200 of anexample self-refresh controller based on SPID. As temperature increases,DRAM storage cell leakage may also increase. Further, temperatures arelikely to increase the higher a memory device is in a stack of memorydevices. In certain embodiments, a DRAM may adjust a self-refresh ratebased on its position in the stack of memory devices in an aim tocounter the increased temperature effects as to storage cell leakage.Also, to the extent that TTSVs or other temperature equalizing methodsare utilized, SPIDs can be used to identify any memory device in thestack that may benefit from an increase in its refresh rate, andaccordingly adjust the refresh rate from a default rate to a higher(e.g., a predetermined) rate.

A standard refresh command (e.g., from address or other control signals)may be detected using refresh command detector 1202. A separateself-refresh counter 1204 (e.g., a wraparound counter) can be used todetermine when a self-refresh cycle should occur. Thus, a refreshoperation can effectively occur when either a refresh command isdetected or a self-refresh counter indicates that it is time for aself-refresh operation. For example, NOR gate 1210 and inverter 1212 canbe used to trigger a refresh operation from either refresh commanddetector 1202 or self-refresh counter 1204.

A self-refresh enable signal (SREN) may be used to enable isolation ofself-refresh oscillator 1206. Thus, if self-refresh is not enabled, SRENmay be low to disable operation of self-refresh oscillator 1206,resulting in a fixed, as opposed to an oscillating, signal at SROSC. IfSROSC is fixed instead of oscillating or clocking, self-refresh counter1204 may not update to get closer to another self-refresh operation.However, if SROSC is oscillating, a rate or frequency of oscillationtherefrom may determine how often self-refresh counter 1204 reaches avalue (e.g., all ‘1’ or logic high levels) that can result in initiationof a refresh operation.

In certain embodiments, self-refresh oscillator adjustor 1208 canreceive SPID bits, and provide an adjustment to self-refresh oscillator1206 in response thereto. For example, the higher the memory device isin the stack of memory devices, as indicated by its SPID, the higher thefrequency of SROSC. This represents one example of how self-refreshfrequency may be increased to help compensate for increased storage cellleakage due to increased temperatures. Of course, one skilled in the artwill recognize that adjustments may also, or alternatively, be made toself-refresh counter 1204 in order to increase a self-refresh frequencyas one goes higher up in a stack of memory devices. Alternatively, asdiscussed above, a device can be configured to change from a defaultrefresh rate to a higher refresh rate based on SPID matching, where thedevice does not necessarily have to be higher in the stack than a givendevice in order to make the adjustment.

Referring now to FIG. 13, shown is a block schematic diagram of anexample self-refresh oscillator adjustment based on SPID. In thisexample, self-refresh oscillator 1206 is adjusted based on SPID bits.This particular example is a five stage oscillator that includes a firststage with PMOS transistor 1306 and NMOS transistor 1308. When enabledby SREN, PMOS transistor 1304 and NMOS transistor 1310 are on, whileNMOS pull-down transistor 1312 is off. Inverter 1302 may invert SREN tocontrol PMOS transistor 1304 and NMOS pull-down transistor 1312. Thus,transistors 1304, 1310, and 1312 may be used to enable or disableself-refresh oscillator 1206 based on enable signal SREN.

The second stage of self-refresh oscillator 1206 may be inverter 1314,and the third stage may include PMOS transistors 1316 and 1320, and NMOStransistors 1322 and 1324. The fourth stage may include PMOS transistors1330 and 1334, and NMOS transistors 1336 and 1338. The fifth stage mayinclude inverter 1344 that drives SROSC and provides feedback to controlthe first stage at transistors 1306 and 1308. Various other transistorsmay be included in order to reduce resistance in a particular path whenenabled, in order to speed up that particular stage. For example, NMOStransistor 1326 can be enabled by SPID[2] such that a pull down paththrough transistor 1322 can be sped up when SPID[2] is high because ofthe parallel resistance effect of transistors 1324 and 1326. SPID[2]being high can indicate that the memory device is in a top half of thestack of memory devices, and SPID[2] being low may indicate that thememory device is in a bottom half of the stack of memory devices. Thus,memory devices in a top half of the stack may have an increasedself-refresh rate based on their SPIDs.

The third stage may also be adjusted via PMOS transistor 1318 which maybe on (by way of inverter 1342) when SPID[1] is high. The fourth stagemay include adjustment PMOS transistor 1332 which can be turned on byway of inverter 1328 when SPID[0] is high. Also, the fourth stage mayinclude adjustment NMOS transistor 1340 that can be turned on whenSPID[1] is high. Table 3 below shows various adjustments in oscillatorstages that can be made based on SPID values.

In this way, a self-refresh oscillator can be adjusted according to SPIDbits. Of course, this represents just one example, and certainembodiments are amenable to a variety of circuit design choices as tohow refresh frequency adjustment can be made based on SPID values. Forexample, different stages can be adjusted in the self-refreshoscillator, and also different numbers of stages can be employed.Further, self-refresh counter 1204 may alternatively, or in addition to,be adjusted based on SPID values. Finally, SPID-based self-refreshfrequency adjustment may supplement other forms (e.g., temperaturesensor-based) of self-refresh adjustment. For example, SPID-basedself-refresh adjustment may represent a coarse tuning, while temperaturesensor-based self-refresh adjustment may represent a finer adjustment,or vice versa.

TABLE 3 Device SPID[2:0] 1326 1318 1340 1332 DRAM-0 000 off off off offDRAM-1 001 off off off on DRAM-2 010 off on on off DRAM-3 011 off on onon DRAM-4 100 on off off off DRAM-5 101 on off off on DRAM-6 110 on onon off DRAM-7 111 on on on on

In particular embodiments, internal regulated supply adjustment can beperformed based on stack position identification. In one embodiment, asemiconductor memory device can include: (i) a stack position identifierfor identifying a position of the semiconductor memory device in analigned vertical stack of a plurality of semiconductor memory devices;(ii) a regulator circuit configured to generate a supply for thesemiconductor memory device; and (iii) a regulator adjustment circuitconfigured to adjust the supply from a first voltage level to a secondvoltage level in response to the stack position identifier when thestack position identifier indicates that the semiconductor memory deviceis higher in the aligned vertical stack than at least one of theplurality of semiconductor memory devices.

Referring now to FIG. 14, shown is a block schematic diagram 1400 of anexample charge pump with VPP level adjustment based on SPID. In thisparticular example, a charge pump design for a word line high (e.g.,greater than VDD+V_(TN)) level can be adjusted based on a position of amemory device in a stack. An oscillating signal (OSC) may be received atinverter 1402 to control a charge pump cycle. NMOS transistor 1412 maybe configured as a capacitor in order to capacitively couple a highlevel to a gate of NMOS transistor 1420 in order to fully precharge mainpumping capacitor 1434 (e.g., an NMOS transistor configured as acapacitor).

When OSC is low, PMOS transistors 1404 and 1408 may be off, while NMOStransistor 1410 may be on to discharge the source/drain side oftransistor 1412, which is connected in a capacitor configuration. Diodeconnected NMOS transistors 1414 and 1416 (when PMOS transistor 1418 isoff) may charge a gate side of transistor 1412 to a level of aboutVDD−2*V_(TN). When OSC is high, NMOS transistor 1410 may be off, whilePMOS transistors 1404 and 1408 may be on in order to charge thesource/drain side of transistor 1412. Through capacitive coupling, thegate of NMOS transistor 1420 may be raised to a level of about2*(VDD−V_(TN)).

Also when OSC is low, and the low level has passed through delay 1422and inverter 1424, inverter 1440 may drive a high level at the gates ofPMOS transistors 1426 and 1430, and NMOS transistor 1432. This maydischarge the source/drain connection of capacitor-connected NMOStransistor 1434. When OSC goes high, after delay 1422, transistors 1426and 1430 may charge the source/drain of 1434 to a VDD level. Theprevious precharge cycle on the gate side of 1434 may have prechargedvia NMOS transistor 1420 (with a gate that is capacitively coupled togreater than VDD+V_(TN)) such that a charge pump action may reach 2*VDDat a gate side of 1434, pumping out of diode connected NMOS transistor1436 to the VPP node a level of about 2*VDD−V_(TN).

Of course, this represents only one example of a possible charge pumpcircuit, and any suitable charge pump or regulating circuit may beadjusted based on a position of the memory device in a stack by usingSPID. In the particular example of FIG. 14, parallel transistors may beused to reduce resistance in a path to improve charge coupling, and/orto shunt the effects of diode connected transistors. As shown, SPID[2]may control PMOS transistor 1418 via inverter 1438 in order to shunt theeffects of diode connected NMOS transistor 1416, which may result in alower precharge level at a gate of transistor 1420, and an associatedlower precharge level at a gate of transistor 1434. As a result, a VPPlevel may be higher for devices in the top half of the stack (e.g., whenSPID[2] is high), and lower for devices in the bottom half of the stack(e.g., when SPID[2] is low).

Other example adjustments can include SPID[0] controlling PMOStransistor 1406, which can reduce the resistance through the pull-uppath for the source/drain connection of 1412 when SPID[0] is low. Also,PMOS transistor 1428 can reduce the resistance through the pull-up pathfor the source/drain connection of main pumping capacitor 1434 whenSPID[1] is low. Table 4 below shows example states of various adjustmenttransistors, which may generally be configured to increase a level ofVPP as one goes up a stack of memory devices.

TABLE 4 Device SPID[2:0] 1406 1418 1428 DRAM-0 000 on off on DRAM-1 001off off on DRAM-2 010 on off off DRAM-3 011 off off off DRAM-4 100 on onon DRAM-5 101 off on on DRAM-6 110 on on off DRAM-7 111 off on off

Of course, other internally regulated supplies (e.g., VBB, VBLR, VREG,etc.) can also be adjusted based on SPID in particular embodiments. Forexample, a word line low level (e.g., to a negative value to reduceleakage effects as temperature increases) may also be adjusted usingSPID values. Further, SPID-based supply regulation adjustment maysupplement other forms (e.g., temperature sensor-based) of regulationadjustment. For example, SPID-based supply adjustment may represent acoarse tuning, while temperature sensor-based supply adjustment mayrepresent a finer adjustment, or vice versa.

In particular embodiments, a chip select valid command detector can bebased on stack position identifier. In one embodiment, a semiconductormemory device can include: (i) a stack position identifier foridentifying a position of the semiconductor memory device in an alignedvertical stack of a plurality of semiconductor memory devices, where theplurality of semiconductor devices are coupled together via a pluralityof common vertical connections; (ii) a receiver configured to receive aplurality of chip select signals from the plurality of common verticalconnections; and (iii) a command detector configured to detect whether acommand is intended for the semiconductor memory device based on acomparison of the received plurality of chip select signals against thestack position identifier.

Referring now to FIG. 15, shown is a block schematic diagram 1500 of anexample chip select and SPID matching circuit. In this example, chipselect match circuits 1502 can be used to compare chip select signalsagainst corresponding SPID bits. For example, CS[0] can be comparedagainst SPID[0] in CSMATCH 1502-0. If both CS[0] and SPID[0] are high,the output of NAND gate 1504 may be low, and NAND gate 1510 may output ahigh. Also, if both CS[0] and SPID[0] are low, the output of NOR gate1506 may be high, the output of inverter 1508 low, and NAND gate 1510may output a high. Thus, if each bit of CS matches each correspondingbit of SPID, NAND gate 1512 may output a low.

SPID_Ready (see, e.g., FIG. 9) being high may indicate that the SPIDsignals are available or enabled for comparison purposes, and thus NANDgate 1514 may effectively act as an inverter. However, if SPID_Ready islow, this may indicate that the SPID signals are somehow not ready ornot enabled for comparison purposes. For example, upon chip power-upand/or when an automatic SPID assignment mode is being used, SPID_Readymay remain low to hold off use of SPID bits until they are settled forthat device. As another example, the SPID_Ready signal may be used toenable a given command (e.g., sent from memory controller 102) for eachmemory device in the stack of devices. In one example, SPID_Ready may berelated to a global chip select signal (e.g., separate from CS[2:0])that enables a command to be accepted in each memory device in thestack. In this way, commands may be presented in a global fashion whereeach device detects the same command, or commands can be applied tocertain devices based on matching of CS bits with corresponding SPIDbits.

Thus when either the SPID signals are not enabled (e.g., SPID_Ready islow), or when a bit-by-bit matching of CS and SPID indicates that acommand is intended for a given memory device, a valid command indicatormay be sent to command detector 1516. In this way, command detector 1516may apply the valid command indicator to a command received (e.g., viaaddress and/or control signals) in order to determine a detectorcommand. Thus, a command received may be ignored by particular device ifany bit of the bit-by-bit matching of CS and SPID results in a mismatch.

Particular embodiments may utilize the common vertical connections (see,e.g., FIG. 2) for each memory device in a stack of devices in order toroute CS signals that can then be compared against SPID on each memorydevice. Thus, for eight memory devices in a stack, only three CS signalsneed be routed in a common vertical connection. Similarly, such decodingcan be employed for any number of memory devices in a stack, as opposedto routing separate vertical connections for each CS signal. Further,default and other command controls can be utilized to control a signalfor bypassing of this comparison of CS to SPID in order to make a givencommand applicable to each memory device in the stack. As one example, atest mode may also be used whereby SPID_Ready or another such enablingsignal may be used to disable chip-specific matching of CS to SPID inorder to allow commands to be applicable to each memory device in thestack.

A chip-level redundancy or de-allocation of a memory device using SPIDsmay also be supported in particular embodiments. If, for example, eventhough KGD testing may indicate that each memory device to be placed inthe stack is good, some failure modes may occur as a result of chipinterconnections or other factors after a device is secured in thestack. In certain embodiments, redundancy or chip disable may beemployed to address failed chips after placement in the stack. Forexample, the chip enable signal may be used to disable further commandsto a given device via command detector 1516 when low. This chip enablesignal may be derived from a latch or other setting that indicates thatthe given chip is to be disabled. In this case, some other deviceoperations (e.g., internal voltage regulation and supply, memory cellreading and writing, etc.) may be disabled, but other device operations(e.g., passing signals between adjacent devices for serially connectedpads, as discussed below) may be maintained.

Further, chip-level redundancy can be employed, such as in case when 9memory devices instead of 8 are placed in the stack, where the extramemory device can be substituted for the bad device by using SPIDs andother controls. For example, address and other control signals may beapplied in a parallel fashion to each memory device in the stack, but DQsignals may be parallelized such that each device contributes a givennumber of DQs (e.g., 64) in order to form a wide I/O (e.g., 512-bitswide) memory structure. Thus, the memory device that provides redundancycan have its DQ signals multiplexed or selected in place of thede-allocated memory device. In this way, the redundant memory device DQsignals may be steered (e.g., using pad selection circuitry as discussedabove with reference to FIG. 4 with an added redundant path pad) toeffectively assume a position of the DQ signals for the de-allocatedmemory device in the stack. In addition, parity bits may also besupported, such as by using a 9^(th) memory device in the stack ofmemory devices in order to supply parity data. In one embodiment, such adevice designated for parity data may instead be allocated as theredundant replacement device in the event of a failure of another memorydevice in the stack.

In particular embodiments, signal latency may also be adjusted based ona position of a device in a stack of devices by using a stack positionidentifier. In one embodiment, a semiconductor memory device caninclude: (i) a stack position identifier for identifying a position ofthe semiconductor memory device in an aligned vertical stack of aplurality of semiconductor memory device; (ii) a latency determinerconfigured to determine a programmed latency from a mode register on thesemiconductor memory device; and (iii) a latency adjustor configured toadjust the programmed latency in response to the stack positionidentifier.

Referring now to FIG. 16, shown is a diagram 1600 of example latencyvariations for stacked memory devices. As seen at a controller (e.g.,memory controller 102) or a common substrate or interface, a time deltadue to latency variations may exist. For example, time delta 1602 mayrepresent a time difference between signal S₀ to/from DRAM-0, ascompared to signal S₇ to/from DRAM-7. In some cases, depending on thenumber of devices in the stack, as well as the TSV 204 and/or die-to-dievia 206 routing, materials used, type of signaling, etc., this timedelay may be significant. In particular, such a time delta or timevariation between memory devices may cause timing problems at a memorycontroller, such as when different DQs are arriving from differentmemory devices as part of a very wide I/O configuration (e.g., 512-bitwide I/O, where 64-bits are coming from each memory device).

Referring now to FIG. 17, shown is a block schematic diagram 1700 of anexample latency adjustment based on SPID. Various latency settings, suchas CAS latency, additive latency, CAS write latency, read latency, etc.,may be programmed into mode register 1702. However, certain embodimentsallow for additional automatic latency adjustments based on SPIDs, whichmay alternatively be stored in mode register 1702, that indicate stackposition. Thus, latency adjustor 1704 may add additional latency as onegoes down a stack of memory devices in order to even out the latency asseen at memory controller 102, or another common interface. In addition,an enable signal (LA_EN) may be used to enable or disable this feature.For example, some applications may have sufficient latency adjustmentsbased on the latency programmed into mode register 1702. However, otherapplications may want automatic stack position based latency adjustmentto occur, and as such LA_EN may be activated so as to allow latencyadjustor 1704 to adjust a programmed latency based on stack position.

In particular embodiments, latency adjustment or alignment can beperformed using a data strobe on a common vertical connection. In oneembodiment, a semiconductor memory device can include: (i) a stackposition identifier for identifying a position of the semiconductormemory device in an aligned vertical stack of a plurality ofsemiconductor memory devices, where the plurality of semiconductordevices are coupled together via a data strobe connection; (ii) a phasedetector configured to detect a phase of the data strobe relative to adata signal; and (iii) a phase adjustor configured to delay the datasignal to match the data strobe, wherein the data strobe is driven byone of the plurality of semiconductor memory devices based on the stackposition identifier.

Referring now to FIG. 18, shown is a cross-section diagram 1800 of anexample shared data strobe signal across stacked DRAMs. In one exampleapproach for automatic latency adjustment, a data strobe signal (e.g.,DS 1802) may be utilized to effectively synchronize data signals basedon a designated memory device in the stack, according to SPID. Eachappropriate data signal for subsequent DRAMs down the stack of memorydevices may adjust a signal phase to match that of the DS signal asdriven by a designated (e.g., DRAM-7) device. In this way, each memorydevice in the stack of memory devices may be synchronized to a DS signalfrom a predetermined one of the memory devices. In addition, directionalcontrol can also be employed whereby the DS signal from one memorydevice (e.g., DRAM-7 on top of the stack) is used for a read ordownstream signaling, and a DS signal from a different memory device(e.g., DRAM-0 at the bottom of the stack) is used for a right orupstream signaling event.

Referring now to FIG. 19, shown is a block schematic diagram 1900 of anexample data strobe pad driver based on a top of stack SPID. In thisexample, DS pad 302-DS may correspond to pad 302 for DS signal 1802 inFIG. 18. Thus, pad 302-DS may represent the external pad or commonvertical connection. Of course, as discussed above, any suitable pad,TSV, die-to-die via, and signal routing arrangement can be accommodatedin certain embodiments. In this example, an internal data strobe signal,which might otherwise be driven onto DS pad 302-DS (e.g., in anon-stacked device usage), can be controlled in certain embodiments suchthat only a predetermined memory device in the stack is allowed to drivepad 302-DS.

In this particular example, a top memory device and a stack of memorydevices may be designated to drive pad 302-DS, and in particular forread or downstream operations. Here, if each of bits in SPID[2:0] arehigh, an output of NAND gate 1904 may be low. This can indicate a topdevice (e.g., DRAM-7 with SPID=111) is allowed to drive pad 302-DSbecause NAND gate 1908 may be enabled by a high input thereto, and NORgate 1912 may be enabled via a low input thereto by way of inverter1910. Then, if the data strobe input is high, an output of NAND gate1908 may be low to drive pad 302-DS high via pull-up PMOS transistor1914. If in this case the data strobe input is low, an output of NORgate 1912 may be high to drive pad 302-DS low via pull-down NMOStransistor 1916.

Driving capability for a given memory device on pad 302-DS may also beenabled when a DS enable (e.g., for a non-stacked device configuration)or test mode signal is activated such that inverter 1902 presents a lowat an input to NAND gate 1906. In this way, a test mode or other DSenable control may be utilised to allow any device, or a particularseparately designated memory device and the stack, to drive pad 302-DS.For other memory devices that do not match SPID[2:0]=111, such as any ofDRAM-0, DRAM-1, . . . DRAM-6, circuit 1900 may be used to tri-state pad302-DS such that the present memory device may not drive this commonvertical connection. In this case, NAND gate 1906 may output a low thatturns off pull-up transistor 1914 via NAND gate 1908, and pull-downtransistor 1916 via NOR gate 1912. In this way, only a predetermined one(e.g., a top memory device in the stack) memory device may drive thecommon connection data strobe signal (e.g., via pad 302-DS) for a givenoperation (e.g., a read operation). Of course, one skilled in the artwill recognize that other types of circuits, as well as otherpredetermined SPID bit inputs can also be employed in certainembodiments.

Referring now to FIG. 20, shown is a block schematic diagram 2000 of anexample data strobe adjustment based on a data strobe driven by, e.g.,the DRAM on the top of the stack of DRAMs. Transition detector 2002 canbe used to detect a transition on a common vertical DS connection (e.g.,at pad 302-DS). For example, the common vertical DS connection may bedriven by a top memory device in the stack, such as by using the driverenable circuitry as discussed above with reference to FIG. 19. In othercases, the common vertical DS connection may be driven by a bottommemory device in the stack, or by another predetermined memory device inthe stack.

Transition detector 2002 may generate a pulse in response to atransition on the common vertical DS signal (labeled “DS pad” in FIG.20). A low to high transition on the DS pad may be detected by thecircuit of NAND gate 2008, delay 2004, and inverter 2006, which canproduce a low going pulse (having a duration of about delay 2004) at anoutput of NAND gate 2008. A high to low transition on the DS pad may bedetected by the circuit of NOR gate 2010, delay 2004, and inverter 2006,which can produce a high going pulse of a duration of delay 2004 at anoutput of NOR gate 2010. The output of NOR gate 2010 can be inverted at2012, and supplied as one input to NAND gate 2014. Thus, the output ofNAND gate 2014 may be a high going pulse generated in response to atransition (either from high to low, or from low to high) on DS pad.

An internally generated data strobe signal can be received at inverter2018, and supplied to a flip-flop circuit. This internally generateddata strobe signal may be a normal such data strobe signal as would begenerated if the memory device were configured for non-stacked usage.The flip-flop circuit can include a first pass gate formed by NMOStransistor 2020 and PMOS transistor 2022, a first latch formed byinverters 2024 and 2026, a second pass gate formed by PMOS transistor2028 and NMOS transistor 2030, and a second latch formed by inverters2032 and 2034. Transistors 2022 and 2030 may be controlled by the outputof NAND gate 2014, and transistors 2020 and 2028 may be controlled by aninverted output of NAND gate 2014 by way of inverter 2016.

In operation, the internally generated data strobe signal can be storedin the first latch when an output of NAND gate 2014 is low. This valuefrom the first latch may be transferred to the second latch when theoutput of NAND gate 2014 is high, such as during the pulse indicatingdetection of a transition on the DS pad. The output of the second latchmay then be inverted at 2036 and provided as an adjusted data strobesignal. In this way, an internally generated data strobe signal can beadjusted to align with a DS pad signal that is driven by another memorydevice (e.g., a memory device at the top of a stack of memory devices).For example, this adjusted data strobe may then be used to clock dataout in a read operation (e.g., at DQ connections) such that data fromeach memory device in the stack essentially arrives at a memorycontroller or common interface chip at substantially a same time.

In this fashion, a data strobe signal on a common vertical connectionmay be used to align signal timing from multiple memory devices at acommon device. The same, or a different, common vertical connection maybe utilised in a write path whereby the signal is driven from memorycontroller 102. In this case, a bottom memory device (e.g., DRAM-0), orsimply the memory controller or logic chip itself, may drive the DSsignal in an upstream signal flow. Then, each memory device of the stackof memory devices may synchronize write data to the DS signal in thesame fashion. In this way, both reads and writes may be effectivelysynchronized among multiple memory devices using a common verticalsignal. Further, any such common vertical signal, or any signal evencommon to two adjacent devices in a stack, may be used in the samefashion to synchronize from one device to another.

In particular embodiments, serially connected signal interconnects amongstacked memory devices may also be accommodated by control of the signalpaths at each memory device in the stack. In one embodiment, asemiconductor memory device can include: (i) a stack position identifierfor identifying a position of the semiconductor memory device in analigned vertical stack of a plurality of semiconductor memory devices;(ii) a first pad coupled to a first signal and a first TSV; (iii) asecond pad coupled to a second signal and a second TSV; and (iv) a padsignal path determiner configured to couple a signal path from the firstpad to the second pad in response to a first state of the stack positionidentifier, and to couple a signal path from the second pad to the firstpad in response to a second state of the stack position identifier.

Referring now to FIG. 21, shown is a cross-section diagram 2100 of anexample serially connected signal through TSVs. A serially connectedsignal as described herein may be one that connects from one memorydevice to another memory device (e.g., adjacent stacked memory devices)in a serial fashion. As shown in the example of FIG. 21, seriallyconnected signal 2102 may include a configuration of pads 302-A and302-B, along with TSVs 204 and/or die-to-die vias 206. In this way, eachmemory device may contain two TSVs allocated to a given signal, but theserialization may be provided by way of die-to-die vias. On-chipsteering circuitry may be used to control driving of a signal to anadjacent upstream device and/or an adjacent downstream device. Incertain embodiments, SPIDs may be used to control such seriallyconnected signal driving.

Serially connected signals as described herein can be any types ofsignals, such as control and/or data signals, that may interface with amemory device. For example, data I/O signals can be serially connected,such as in a master-slave data arrangement. In another example, each orsubstantially all data and/or control signals can be serially connectedbetween the memory devices so as to avoid long TSV and/or die-to-die viaconnections across several devices. In this way, clocking and controlcan be passed from one memory device to another in serial fashion.Further, pads as described herein can represent any suitableinterconnect positions or interfaces on a semiconductor device.

Referring now to FIG. 22, shown is a schematic diagram 2200 of examplepad drivers for a serially connected signal through TSVs. This examplemay be applicable for upstream signals; that is, signals flowing frommemory controller 102 upstream through each memory device until reachinga top memory device in the stack. Viewed in conjunction with the exampleof FIG. 21, the example of FIG. 22 shows on-chip control for receiving asignal at one pad (or interconnect position), and directing that signalto another pad (or interconnect position), where the direction of thesignal path is alterable depending on SPID values. More specifically,for an even-numbered memory device in the stack of memory devices,SPID[0] may be ‘0’, which may enable an output driver for pad 302-B anddisable an output driver for pad 302-A. Similarly, for an odd-numberedmemory device in the stack a memory devices, SPID[0] may be ‘1’, whichmay enable an output driver for pad 302-A, and disable an output driverfor pad 302-B. Further, receivers for each pad may be activatedregardless of SPID or even/odd values.

In the example of FIG. 22, the tri-statable driver for pad 302-A caninclude pull-up PMOS transistor 2206-A, pull-down NMOS transistor2208-A, NAND gate 2204-A, NOR gate 2212-A, and inverter 2210-A. Thereceiver path from pad 302-B can include inverters 2218 and 2220.Inverter 2218 may represent any suitable type of receiver circuit forreceiving a signal from pad 302-B, and converting to full CMOS levels(e.g., including inverter 2220, and labeled pad B input). Similarly, thetri-statable driver for pad 302-B can include pull-up PMOS transistor2206-B, pull-down NMOS transistor 2208-B, NAND gate 2204-B, NOR gate2212-B, and inverter 2210-B. The receiver path from pad 302-A caninclude inverters 2214 and 2216. Inverter 2214 may represent anysuitable type of receiver circuit for receiving a signal from pad 302-A,and converting to full CMOS levels (e.g., including inverter 2216, andlabeled pad A input).

In certain embodiments, a state of SPID[0], which may indicate an evenor odd numbered memory device position in the stack, can be used todetermine a direction of the signal path. For example, an even-numberedmemory device may receive a signal from pad 302-A and send the signal topad 302-B, while an odd-numbered memory device may receive a signal frompad 302-B and send the signal to pad 302-A. A true value of SPID[0] canbe used to enable the tri-statable driver for pad 302-A, while acompliment of value of SPID[0] can be used (e.g., via inverter 2202) toenable the tri-statable driver for pad 302-B.

Thus, SPID values (e.g., a state of SPID[0]) can be used to effectivelysteer a signal from one pad to another, particularly when that signal ispart of a serially connected path, such as that shown in FIG. 21. Ofcourse, other signal paths, arrangements, components of a signal path(e.g., other than pads, die-to-die vias, etc.) may be included inparticular embodiments. Also, other serial connections, such as from onememory device to another memory device that is not adjacent thereto, mayalso be accommodated in particular embodiments. Further, other circuitrybetween or around pads or other external connection interfaces (e.g.,ESD circuitry) may also be used in certain embodiments.

Referring now to FIG. 23, shown is a schematic diagram 2300 of examplepad drivers for a serially connected signal through TSVs with on-chipsignal modifications. In this example, a pad A input signal at theoutput of inverter 2216 may be modified 2302 prior to being sent to thetri-statable buffer for pad 302-B. Similarly, a pad B input signal atthe output of inverter 2220 may be modified 2304 prior to being sent tothe tri-statable buffer for pad 302-A. Such modifications can includeany logical or logic circuit or control modifications to the signal. Forexample, some signals may be gated by other control signals prior tobeing passed to a next memory device along the serially connected path(e.g., serially connected signal 2102). As another example, master-slavecontrol (e.g., of a data or DQ signal for one device relative to anadjacent device in the stack) can also be implemented in modificationblocks 2302/2304.

As one example use of signal modifiers (e.g., via 2302 or 2304), phasedifferences can be determined between signals propagating via one ormore memory devices in the stack. Then, latency may be added whereappropriate in order to adjust and synchronize signaling across memorydevices. In another example, a clock frequency may be set during test,with counting of clocks based on SPID values, and may be used todetermine a latency difference between memory devices (e.g., adjacentdevices) in a memory stack. The signal modifiers may also be used toprovide results of a capacitance comparison test, such as discussedabove with reference to FIGS. 7 and 8, for a pair of pads (e.g., pads A& B, or other pads, etc.).

Test modes may also make use of, or otherwise be incorporated with,signal modifiers (e.g., via 2302 and/or 2304), such as for boundary scanor other design for test (DFT) applications. The signal modifiers canemploy any number of logical combinations, test registers, and the like.For example, test registers may be read out from one of pad A or pad B,and passed to the other as part of a test mode. Oscillation modes mayalso be created in this fashion by using the signal modifiers to inverteach signal as it passes through a given memory device. In this way,clocking can occur across multiple memory devices in a stack of memorydevices. For example, the serially connected signal may enter a chipwith a high value, and send a low value to an adjacent chip, which thensend a high value to its adjacent chip, and so on, thus creating across-chip clock. Also, one serially connected signal path may bedesignated or used as such a cross-chip clock signal for an upstreampath, while another such serially connected signal path may bedesignated or used as a cross-chip for a downstream path. A cross-chipclocking loop may also be formed by connecting the upstream cross-chipclock path to the downstream cross-chip clock path at a designatedmemory device (e.g., a top memory device in the stack). Such cross-chipclocking may be particularly useful for test modes that test acrossdifferent memory devices, including those that test memory devices in astack.

Referring now to FIG. 24, shown is a schematic diagram 2400 of examplebi-directional pad drivers based on upstream or downstream signaling fora serially connected signal through TSVs. In this example, the driverdirectional control may be changed based on whether the signaling isupstream or downstream for this particular serially connected signalpath. If the serially connected signal (e.g., 2102) is for an upstreamsignal path, the pass gate formed by NMOS transistor 2408 and PMOStransistor 2410 may be turned on by the upstream indicator signal, andits complement via inverter 2412. The upstream indicator being activatedcan allow for SPID[0] to control the tri-statable driver for pad 302-A,and the compliment of SPID[0] (via inverter 2414) to control thetri-statable driver for pad 302-B. Thus, when the upstream indicator isactive, the circuit of FIG. 24 may operate substantially as that of theexample in FIG. 23.

However, if the serially connected signal (e.g., 2102) is for adownstream signal path, the pass gate formed by NMOS transistor 2404 andPMOS transistor 2406 may be turned on by the upstream indicator signalbeing low. The upstream indicator being low can allow for the complimentof SPID[0] (e.g., via inverter 2402) to control the tri-statable driverfor pad 302-A, and the true value of SPID[0] (via inverter 2414) tocontrol the tri-statable driver for pad 302-B. Thus, when the upstreamindicator is inactive or low, indicating that the signal associated withthe serially connected signal path is a downstream signal, even-numberedmemory devices may send the signal from pad B to pad A, whileodd-numbered memory devices may send the signal from pad A to pad B.

In this way, serially connected signal paths that employ TSVs and twopossible external connection positions or pads on each memory device,may be configured to flow through a given device in a direction that iscontrolled by SPID bits. Of course, depending on the particular patternsof TSVs and/or die-to-die vias, other bits of SPID values could beemployed. For example, a signal may be in a common vertical connectionposition for a bottom half of the memory devices, and can switch over toanother common vertical connection position for a top half of the memorydevices, or any combination thereof. Based on the particular pattern andtype of signaling (e.g., upstream, downstream, modifiable, etc.),different SPID bit values can be used to control the directional flow ofthe signal through a given memory device.

In particular embodiments, a content-addressable memory (CAM) device maybe configured for serial searching in a stacked arrangement. In oneembodiment, a method of controlling a search in a first CAM device caninclude: (i) receiving a search key and a search control signal from asecond CAM device, where the second CAM device is a next CAM devicebelow the first CAM device in an aligned vertical stack of a pluralityof CAMs devices; (ii) performing a search of the first CAM device inresponse to the received search key and the received search controlsignal; (iii) sending the search key and the search control signal fromthe first CAM device to a third CAM device if the search of the firstCAM device results in no match on the first CAM device, where the thirdCAM device is a next CAM device above the first CAM device in thealigned vertical stack of the plurality of CAMs devices; and (iv)sending a search result to the second CAM device if the search of thefirst CAM device results in a match on the first CAM device.

Referring now to FIG. 25, shown is a cross-section diagram 2500 ofexample CAM devices with serially connected search key and search resultsignals. In this particular example, eight CAM devices are shown, andeach may utilize stack position identifiers as discussed herein. Asdiscussed, any type of memory device or repeated chip in a stack of suchdevices can be accommodated in particular embodiments. Also, any numberof such stacked memory devices may also be accommodated, with anassociated adjustment in SPID bits. In the particular example of FIG.25, a search key 2502 can include upstream type serially connectedsignals. For example, search key 2502 can include upstream seriallyconnected signals such that each CAM device may pass the search key upto a next CAM device when that next CAM device is to perform a search.

In order to save power, if a search of a given CAM results in a matchcondition, that CAM can send the search results downstream via seriallyconnected signals 2504. Thus, if a search key is presented to CAM-0, anda search is performed on CAM-0 that results in no matches, CAM-0 canthen forward the search key upstream to CAM-1 so that CAM-1 can performa search. This can continue until a particular CAM obtains a match andsearch result from the search using the search key. The CAM with thematch can then send the search results downstream, without notifying anyfurther upstream CAM devices. This has the advantage of saving power bynot having to search each CAM device in a stack of such CAM devices. Inaddition, a priority based on stack position is also provided because ofthe order of performing searches. For example, CAM-0 may be a higherpriority than CAM-1, and CAM-1 may be a higher priority than CAM-2, andso on up the stack of CAM devices.

Referring now to FIG. 26, shown is a flow diagram of an example methodof performing searches and providing results for stacked CAM devices. In2600, an example flow for a CAM device that is to perform a search isshown. The flow begins (2602), and at 2604 a search key can be receivedfrom a downstream chip. At 2606, a search can be performed using thereceived search key. If there is a match (2608), at 2610 the searchresults can be sent to a downstream chip, completing the flow at 2614.However, if there is not a match (2608), at 2612 the search key may besent upstream (e.g., search key 2502) to allow that upstream chip toallow that upstream chip to perform a search, completing the flow at2614.

In 2650, an example flow for a CAM device that has already performed asearch on a given search key, and resulted in no match, as shown. Theflow begins (2652), and at 2654 a search result is received from anupstream chip. Because the given CAM device has already been searchedusing the given search key, thus the search key may be passed downstreamon a serially connected signal path (e.g., search results 2504). Thus at2656, the search result may be sent to a downstream chip, completing theflow at 2658.

Other CAM functions that can be performed in a sequential fashion byusing serially connected signals as described herein, may also besupported in particular embodiments. For example, reads and writes ofvalues to the CAMs may be performed in a sequential fashion,particularly when considering pipelining or interleaving various typesof operations, such as reads/writes mixed in with search operations. Inone example, in order to maintain timing consistency, search operationsmay be passed through to each device up the stack and returned from atop device in the stack. For example, even if a search of CAM-3 resultsin a match to the search key, the search key may still propagate up thestack of CAM devices to reach CAM-7, but with a flag set that indicatesthat no actual search is to be performed on CAM-4, CAM-5, CAM-6, orCAM-7. For example, such a flag may be applied on another commonvertical connection (e.g., a command signal), or may be encoded withinsearch key 2502.

Alternatively, a count of clock cycles may be made in the CAM devicehaving a match of the search key (e.g., CAM-3), and search results 2504can be driven by CAM-3 at an appropriate time or clock cycle consistentwith the search result being driven by the top CAM in the stack (e.g.,CAM-7). In either the clock cycle delay, or the actual propagation up toa top CAM and back, additional CAM device searches (e.g., those CAMsabove CAM-3 in the stack) may still be suppressed in order to savepower. Also, strobe signals can also be employed as discussed above inorder to synchronize results from one camp to another CAM. Thus, aconsistent number of clock cycles may be designated to a search functionno matter which CAM in the stack provides the search result. While thisincreases a latency of a search result for each search except those thatonly find a match in the top CAM in the stack, a consistent latency canallow for deeper pipelining of CAM operations.

In another example of search functionality for stacked CAM devices, asearch key may be applied to each of the CAM devices in parallel. Then,each CAM in the stack may hold this search key until receiving noticefrom a CAM position below that CAM in the stack of CAMs. For example,CAM-4 may hold the received search key until receiving an indicationfrom CAM-3 that a search on this search key has resulted in no match,and thus CAM-4 may proceed with a search on that search key. In thisapproach, fewer signals may be of the serially connected variety, andsearch key signals may be direct or parallel connected common verticalsignals, which may help to reduce CAM chip size.

In another variation, each CAM in the stack of CAMs may hold a suppliedsearch key for possible searching on that CAM for a predetermined numberof clock cycles based on the SPID of that CAM device. This predeterminednumber of clock cycles may include a number of clock cycles that ittakes to perform a search operation on a CAM device multiplied by anumber representing the stack position via the SPID. For example, if ittakes five clock cycles to perform a CAM search, CAM-3 may perform asearch of a given search key after 15 clock cycles, upon receiving anindication that none of CAM-0, CAM-1, nor CAM-2 have found a match tothe given search key. In this way, CAM operations can be serialized andsynchronized for multiple CAM devices in a stack of such devices.

In addition to stacks of memory devices that include a single type ofmemory device, hybrid structures that include at least two differenttypes of memory devices are also contemplated. For example, one or moreSRAMs may be coupled to one or more DRAMs in a stack of such devices. Inone example, one or more DRAMs may be stacked on top of one SRAM, andthis pattern may be replicated (e.g., one SRAM, followed by three DRAMs,followed by another SRAM, and then another three DRAMs). Such a memorydevice arrangement may be applicable to cache functionalities and/orapplications. Further, SPIDs associated with such hybrid memory devicestack structures may include one identifier per repeatable pattern(e.g., one SRAM and three DRAMs), or designated bits (e.g., the twoleast significant bits) that indicate a specific memory device within arepeatable pattern of memory devices.

As another example hybrid memory device stack structure, a CAM devicemay be followed by one or more DRAMs devices in a repeatable pattern.With this structure, the DRAMs may be configured to perform CAMoperations, or extended search operations, such as when a given CAM doesnot find a match case. For example, the CAM devices in this repeatablepattern may operate much as discussed above, but a mismatch may firstresult in a search of associated DRAM devices, prior to being sent to anext CAM device up the stack of memory devices. Further, the DRAMsassociated with a given CAM may also be searched in a sequential order.As can be appreciated by one skilled in the art, any suitable variety ofmemory devices may be stackable, and identifiable via stack positionidentifiers as discussed herein.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilise theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A semiconductor memory device, comprising: a plurality of pads allocated to a data input/output (DQ) signal on the semiconductor memory device; a stack position identifier configured to identify a position of the semiconductor memory device in an aligned vertical stack of a plurality of semiconductor memory devices; and a pad selector configured to select one of the plurality of pads to be connected to the DQ signal on the semiconductor memory device in response to the stack position identifier, wherein the pad selector is further configured to disconnect each of a remaining of the plurality of pads from the DQ signal based on the stack position identifier.
 2. The semiconductor memory device of claim 1, wherein the pad selector comprises a plurality of pass gates corresponding to the plurality of pads, and wherein each of the pass gates is configured to be controlled by a decoded version of the stack position identifier.
 3. The semiconductor memory device of claim 1, wherein the selected one of the plurality of pads is different for each of the plurality of semiconductor memory devices in the aligned vertical stack.
 4. The semiconductor memory device of claim 1, wherein the plurality of pads represent different positions that are configured for interconnection from the semiconductor memory device to another of the plurality of semiconductor memory devices in the aligned vertical stack.
 5. The semiconductor memory device of claim 1, wherein the pad selector is configured to steer a redundant pad path to the selected pad.
 6. The semiconductor memory device of claim 1, wherein the pad selector comprises devices configured for electrostatic discharge (ESD) protection.
 7. The semiconductor memory device of claim 1, wherein an adjacent pad in the plurality of pads is selected for an adjacent semiconductor memory device in the aligned vertical stack.
 8. The semiconductor memory device of claim 1, wherein the stack position identifier is configured to be stored in nonvolatile memory on the semiconductor memory device.
 9. The semiconductor memory device of claim 1, wherein at least one of the plurality of pads is connected to a through-silicon via (TSV).
 10. A method of selecting pads of a semiconductor memory device, the method comprising: allocating a plurality of pads to a data input/output (DQ) signal on the semiconductor memory device; identifying, by a stack position identifier, a position of the semiconductor memory device in an aligned vertical stack of a plurality of semiconductor memory devices; selecting, in response to the stack position identifier, one of the plurality of pads to be connected to the DQ signal on the semiconductor memory device; and disconnecting, in response to the stack position identifier, each of a remaining of the plurality of pads from the DQ signal.
 11. The method of claim 10, wherein the selected one of the plurality of pads is different for each of the plurality of semiconductor memory devices in the aligned vertical stack.
 12. The method of claim 10, wherein the plurality of pads represent different positions that are configured for interconnection from the semiconductor memory device to another of the plurality of semiconductor memory devices in the aligned vertical stack.
 13. The method of claim 10, further comprising steering a redundant pad path to the selected pad.
 14. The method of claim 10, wherein an adjacent pad in the plurality of pads is selected for an adjacent semiconductor memory device in the aligned vertical stack.
 15. The method of claim 10, wherein at least one of the plurality of pads is connected to a through-silicon via (TSV).
 16. An apparatus having an aligned vertical stack of a plurality of semiconductor memory devices, the apparatus comprising for each semiconductor memory device: a plurality of pads allocated to a data input/output (DQ) signal on the semiconductor memory device; a stack position identifier configured to identify a position of the semiconductor memory device in the aligned vertical stack of the plurality of semiconductor memory devices; and a pad selector configured to select one of the plurality of pads to be connected to the DQ signal on the semiconductor memory device in response to the stack position identifier, wherein the pad selector is further configured to disconnect each of a remaining of the plurality of pads from the DQ signal based on the stack position identifier.
 17. The apparatus of claim 16, wherein the pad selector comprises a plurality of pass gates corresponding to the plurality of pads, and wherein each of the pass gates is configured to be controlled by a decoded version of the stack position identifier.
 18. The apparatus of claim 16, wherein the selected one of the plurality of pads is different for each of the plurality of semiconductor memory devices in the aligned vertical stack.
 19. The apparatus of claim 16, wherein a through-silicon via (TSV) is configured to connect the DQ signal between a first of the plurality of semiconductor memory devices and a second of the plurality of semiconductor memory devices in the aligned vertical stack, and wherein the DQ signal is coupled to at least one of the plurality of pads.
 20. The apparatus of claim 16, wherein the plurality of pads represent different positions that are configured for interconnection from the semiconductor memory device to another of the plurality of semiconductor memory devices in the aligned vertical stack. 